Flasher control circuit



United States Patent Inventors Adam L. Keller Michigan City; Marvin R.Baugh, LaPorte County, Ind. Appl. No. 783,614 Filed Nov. 16, 1967Patented Dec. 29, 1970 Assignee Meridian Industries, Inc.

a corporation of Delaware. by mesne assignments FLASHER CONTROL CIRCUIT6 Claims, 1 Drawing Fig.

U.S. Cl 317/16, 307/247, 307/305; 315/200; 317/33 Int. Cl 1105b 37/03;H02h 3/08 Field olSearch 315/200.1;

IBM Technical Disclosure Bulletin 307-305 Vol. 2, No. 5, Feb. 1960 6.15.Olson Primary Examiner.lames D. Trammell Attorney-Dale A. WinnieABSTRACT: A flasher circuit including a silicon controlled rectifierserving as a switching means and having a low cost transistor with asaturation level lower than the holding voltage of the switchingrectifier in shunt connected operative control thereacross.

ca CR CR R9 14 L1 rn'n+ scm Tics (g/0 f {new I 1 FLASHER CONTROL CIRCUITBACKGROUND OF THE INVENTION trols, inconsistent supplyvoltages becauseof other electrical equipment used,and because of the constant moistureand humidity problem in fording streams, traveling through low marshlands, etc.

To obviate some of these problems, transistorized flasher circuits havebeen devised for military use, with internally reactive circuit breakingmeans, waterproofed and sealed housings, including cooling fins fordissipating desertlike heat, etc. However, the two major problems, whichhave been insurmountable, at least on a low cost basis, until now, havebeen in protecting the control rectifier circuit against shortingoverloads, by accidental or military damage, and in avoiding high levelnoise interference in the system'which can cause erratic action.

Although silicon controlled rectifiers are known to have sufficientlyhigh inherent current passing capabilities to permit use of a fuse orcircuit breaker in the primary power circuit, to guard against shorts inthe lamp leads,,no satisfactory low cost means have been available,heretofore, for turning the latter off and which is itself free of shortcircuiting damage.

SUMMARY OF THE INVENTION The present invention relates to flashercircuits for signal and warning lights, particularly suited formilitaryuse, and which includes a transiatorized circuit with protection againstshorting overloads and high level noise interference.

A silicon controlled rectifier is used as a switching device for theflasher circuit which includes a free-running multivibrator timingcircuit with a regulator and filter section to assure a constant cyclingrate and to eliminate high frequency noise effects. Separate circuitmeans are used to turn the silicon contnolled rectifier on, in accordwith positive going pulses, and to-turn it off at the end of each cycle.The means for turning off the silicon controllednrectifier is agermanium power transistor, of nominal expense, having a lowersaturation voltage than the holding voltage of the silicon controlledrectifier and which is shunt connected across it and is in circuit withmeans providing a reverse base-to-emitter bias voltage at the germaniumpower transistor, so that it is inoperative until needed to turn theswitching device off, I

These and other objects and advantages will be better known andappreciated upon consideration of the detailed description of apreferred embodiment of the invention set forth hereinafter, followingreference to the accompanying drawing.

DESCRIPTION or THE RAWING The single F IG. drawing is a schematic of theelectrical circuit for a military approved type of short-proof signallight flasher.

DETAILED DESCRIPTION The flasher circuit shown in the drawing, and whichillustrates a preferred embodimentof the present invention includes sixbasic sections or component parts.

The first section include the silicon controlled rectifier SCRI, whichserves as the s itching device, connected in series with the lamp load'10, to control current flow therethrough, and provided in the conductorline 12 between the power source lead 14 and the ground connection 16.

The second section is the timing circuit to control the cycling rate ofthe switching device (the. silicon controlled rectifier SCRl) andincludes the signal transistors 01 and '02, the resistors R1, R2, and R3and R4, and the capacitors C1 and C2. Together they provide a freerunning multivibrator with the component values selected for the desiredcycling rate, which in this instance is about 90 cycles per minute.

The transistors Q1 and. 02 are connected to the power source line 14,and have their bases connected to resistors R3 and R2 and theircollectors to resistors R1 and R4, respectively. The capacitors C1 andC2 bridge the conductor leads including resistors Rl-R2 and R3-R4,respectively, and the resistors are all connected to a common lead 18into the regulator section of the third component section of the flashercircuit. 1

The third section includes both a regulator and a filter section toassure a constant cycling rate despite variation in supply voltage oradverse effects due to high frequency noise. The regulator is of theseries type and includes transistor Q3, Zener diode CR2 and resistor R5;with the output voltage for the Zener diode, in this instance, 8.2volts. The filter section connected in series by lead 20 to the gatecontrol of rectifier.

SCRl, resistor R12 connected ahead ,of resistor R11 and to ground line16, and resistor R10 connected between the gate connection and lead 12ahead of the lamp load. The capacitor C4 is connected between thecollector of transistor 01 and resistor R1, at the junction connectionfor capacitor C1, and

together with resistor R12 serves to differentiate the positive goingpulse formed at the collector of transistor O1 to turn on the rectifierSCRl and illuminate the lamp load 10; the rectifier CR4 allowing onlypositive going pulses to pass the gate lead of the switching rectifierSCRl.

' The means for tuming' off the switching rectifier SCRl, at the end ofits cycle, is in the fifth section ofthe circuit and includes agermanium power transistorQS in a shunt connection 22 between the powersource lead 14 and the cathode of the switching rectifier. i

The germanium power transistor 05 has-an appreciably lowercollector-to-emit ter saturation level than the holding voltage for theswitching rectifier SCRl and is accordingly biased in a normally ofistate, as will subsequently be described, so that it shunts out andshuts off the switching which is in turn connected through its own baseto the collector of transistor Q2, through capacitor C5 and resistor R6.

. The duration of the drive pulse is controlled by the values ofcapacitor C5 and resistor R6 which together with resistor R7, connectedto ground, serves as a differentiator.

The sixth section of the circuit includes means for providing a reversebase-to-emitter bias at transistor Q5, which keeps it turned off excepton signal, and enables the use of a much lower cost control device andone which is better suited to meet the high temperature requirements formilitary use.

The off-bias circuit for the low cost germanium transistor Q5includesrectifiers CR5 and CR6, connected in the timing circuit to thebases of transistors 01 and O2, to sample the voltage level there at andto charge capacitor C3 through lead 23 to a level which provides thebias polarity through conductor 24 and through resistor R9 to thebase-to-emitter junction of transistor Q4,.and permits high temperatureoperation of the latter.

The pulse of current furnished by transistor 04 through resistor R8overrides this off-bias and will turn the transistor 05 Otherwise, thebias holds the shunt connection inoperative and thelow power transistoroff until needed.

As long as a fuse or circuit breaker of appropriate rating is i used inthe primary power circuit the flasher circuit will not be damagedibyaccidental shorts in the lamp leads, due to the inherent'high currentpassingfc'apabilities of silicon controlled rectifiers.

l.' In a short-proof circuit for a silicon control rectifier operabletoenergize a signal light flasher, the improvements comprising: a g

a first means operable to condition the silicon control rectifier foroperation; w a power transistor operable to condition the siliconcontrol rectifier inoperative, being connected across the siliconcontrol rectifier, and having a collector-to-emitter saturation levellower than the holding voltage of the silicon control rectifiernecessary for operation of the silicon control rectifier;

a second means operable to condition the power transistor inoperative,said second means providing an inactivating bias on the powertransistor;

a third means operable to condition said second means inoperative byoverriding the inactivating bias on the power transistor; and

said third means being electrically connected to said first means andbeing operable in response to the operation of said first means at adelayed time subsequent to the operation of said first means.

I 2. The circuit of claim 1, and said second means including .sistorproviding the delayed rectifiers connected to said first means, andincluding a capacitor alternately charged by said rectifiers and saidcapacitor being in a bias-providing connection with the powertransistor.

3 The circuit of claim Land said first means having a capacitor and aresistor in series, and said capacitor and retir'ne 'in'accordance withthe values thereof. 1

4. The circuit of claim 1 wherein said first means comprises a firstcapacitor and a resistor in series; said first capacitor and saidresistor providing the delayed time inaccordance with the valuesthereof, and wherein said second' meanscomprises rectifiers connected tosaid first means; and including a second capacitor alternately chargedby said rectifiers, and said capacitor being in a bias-providingconnection with the power transistor. i

5. The circuit of claim 1, and said first means comprising afree-running, series-type, multivibrator operable to condition thesilicon control rectifier for operation, and further comprising aregulator and filter section for providing a-constant cycling rateunaffected by the supply of voltage and highfrequency noise variations.I I

6. The circuit of claim 4, wherein saidfirst means also comprises afree-running series-type multivibratoroperable to condition the siliconcontrol rectifiers foroperation, said first means further. comprising aregulator and filter section for providing a constant cycling rateunaffected by. the supply of voltage and high-frequency noisevariations.

